Response rates among control subjects in case-control studies

An Integrated Approach for the Early Detection of Endometrial and Ovarian Cancers (Screenwide Study): Rationale, Study Design and Pilot Study

Screenwide is a case-control study (2017−2021) including women with incident endometrial and ovarian cancers (EC and OC), BRCA1/2 and MMR pathogenic variant carriers, and age-matched controls from three centers in Spain. Participants completed a personal interview on their sociodemographic factors, occupational exposure, medication, lifestyle, and medical history. We collected biological specimens, including blood samples, self-collected vaginal specimens, cervical pap-brush samples, uterine specimens, and, when available, tumor samples. The planned analyses included evaluation of the potential risk factors for EC/OC; evaluation of molecular biomarkers in minimally invasive samples; evaluation of the cost-effectiveness of molecular tests; and the generation of predictive scores to integrate different epidemiologic, clinical, and molecular factors. Overall, 182 EC, 69 OC, 98 BRCA pathogenic variant carriers, 104 MMR pathogenic variant carriers, and 385 controls were enrolled. The overall participation rate was 85.7%. The pilot study using 61 samples from nine EC cases and four controls showed that genetic variants at the variant allele fraction > 5% found in tumors (n = 61 variants across the nine tumors) were detected in paired endometrial aspirates, clinician-collected cervical samples, and vaginal self-samples with detection rates of 90% (55/61), 79% (48/61), and 72% (44/61) by duplex sequencing, respectively. Among the controls, only one somatic mutation was detected in a cervical sample. We enrolled more than 800 women to evaluate new early detection strategies. The preliminary data suggest that our methodological approach could be useful for the early detection of gynecological cancers.

Identifying family and unpaid caregivers in the electronic health record: A descriptive analysis (Preprint)

Background

Most efforts to identify caregivers for research use passive approaches such as self-nomination. We describe an approach in which electronic health records (EHRs) can help identify, recruit, and increase diverse representations of family and other unpaid caregivers.

Objective

Few health systems have implemented systematic processes for identifying caregivers. This study aimed to develop and evaluate an EHR-driven process for identifying veterans likely to have unpaid caregivers in a caregiver survey study. We additionally examined whether there were EHR-derived veteran characteristics associated with veterans having unpaid caregivers.

Methods

We selected EHR home- and community-based referrals suggestive of veterans’ need for supportive care from friends or family. We identified veterans with these referrals across the 8 US Department of Veteran Affairs medical centers enrolled in our study. Phone calls to a subset of these veterans confirmed whether they had a caregiver, specifically an unpaid caregiver. We calculated the screening contact rate for unpaid caregivers of veterans using attempted phone screening and for those who completed phone screening. The veteran characteristics from the EHR were compared across referral and screening groups using descriptive statistics, and logistic regression was used to compare the likelihood of having an unpaid caregiver among veterans who completed phone screening.

Results

During the study period, our EHR-driven process identified 12,212 veterans with home- and community-based referrals; 2134 (17.47%) veteran households were called for phone screening. Among the 2134 veterans called, 1367 (64.06%) answered the call, and 813 (38.1%) veterans had a caregiver based on self-report of the veteran, their caregiver, or another person in the household. The unpaid caregiver identification rate was 38.1% and 59.5% among those with an attempted phone screening and completed phone screening, respectively. Veterans had increased odds of having an unpaid caregiver if they were married (adjusted odds ratio [OR] 2.69, 95% CI 1.68-4.34), had respite care (adjusted OR 2.17, 95% CI 1.41-3.41), or had adult day health care (adjusted OR 3.69, 95% CI 1.60-10.00). Veterans with a dementia diagnosis (adjusted OR 1.37, 95% CI 1.00-1.89) or veteran-directed care referral (adjusted OR 1.95, 95% CI 0.97-4.20) were also suggestive of an association with having an unpaid caregiver.

Conclusions

The EHR-driven process to identify veterans likely to have unpaid caregivers is systematic and resource intensive. Approximately 60% (813/1367) of veterans who were successfully screened had unpaid caregivers. In the absence of discrete fields in the EHR, our EHR-driven process can be used to identify unpaid caregivers; however, incorporating caregiver identification fields into the EHR would support a more efficient and systematic identification of caregivers.

Trial Registration

ClincalTrials.gov NCT03474380; https://clinicaltrials.gov/ct2/show/NCT03474380

Evaluation of Nonresponse Bias in a Case-Control Study of Pleural Mesothelioma

Nonparticipation limits the power of epidemiological studies, and can cause bias. In a case–control study on pleural malignant mesothelioma (MM), we found low participation in interviews (63%) among controls. Our goal was to characterize nonresponder controls and assess nonresponse bias in our study. We selected all nonresponder controls (204) and a random sample of responder controls (174). Data were obtained linking hospital admissions and town registrars, and concordance between sources was assessed. Nonresponse bias was evaluated using a logistic regression model applying the inverse probability weighting approach. The odds ratio (OR) for the status of the respondents was 0.61 (95% confidence interval (CI): 0.33–1.16) for controls aged 61–70, 0.37 (CI: 0.20–0.66) for those aged 71–80, and 0.40 (CI: 0.20–0.80) for those aged above 80 (reference group: ≤60 years). Controls with low education level had lower OR (0.47; CI: 0.26–0.84). After adjustment, the ORs for MM by categories of cumulative exposure to asbestos were similar to the unadjusted results, ranging from 4.6 (CI: 1.8–11.7) for cumulative exposures between 0.1 and 1 f/mL-y to 57.5 (CI: 20.2–163.9) above 10 f/mL-y. Responder controls were younger and had higher education level. Nevertheless, there was little evidence of bias from nonresponse in the risk estimates of MM.

Practice of reporting social characteristics when describing representativeness of epidemiological cohort studies - A rationale for an intersectional perspective

Representativeness has been defined as the degree of similarity of a study population compared to an external population. To characterize a study population, both health-related and social or demographic features should be considered according to current guidelines. However, little guidance is given on how to describe social complexity of study populations when aiming to conclude on representativeness. We argue that sociological concepts should inform characterizations of study populations in order to increase credibility of conclusions on representativeness. The concept of intersectionality suggests to conceptualize social location as a combination of characteristics such as sex/gender and ethnicity instead of focusing on each feature independently. To contextualize advantages of integrating the concept of intersectionality when investigating representativeness, we reviewed publications that described the baseline population of selected epidemiological cohort studies. Information on the applied methods to characterize the study population was extracted, as well as reported social characteristics. Nearly all reviewed studies reported descriptive statistics of the baseline population and response proportions. In most publications, study populations were characterized according to place of residence, age and sex/gender while other social characteristics were reported irregularly. Differential patterns of representativeness were revealed in analyses that stratified social characteristics by sex/gender or age. Furthermore, the included studies did not explicitly state the theoretical approach that underlay their description of the study population. Intersectionality might be particularly fruitful when applied to descriptions of representativeness, because this concept provides an understanding of social location that has been developed based on situated experiences of people at the intersection of multiple axes of social power relations. An intersectional perspective, hence, contributes to approximate social complexity of study populations and might contribute to increase validity of conclusions on representativeness of population-based studies.

Using statutory health insurance data to evaluate non-response in a cross-sectional study on depression among patients with diabetes in Germany

BACKGROUND

Low response rates do not indicate poor representativeness of study populations if non-response occurs completely at random. A non-response analysis can help to investigate whether non-response is a potential source for bias within a study.

METHODS

A cross-sectional survey among a random sample of a health insurance population with diabetes (n = 3642, 58.9% male, mean age 65.7 years), assessing depression in diabetes, was conducted in 2013 in Germany. Health insurance data were available for responders and non-responders to assess non-response bias. The response rate was 51.1%. Odds ratios (ORs) for responses to the survey were calculated using logistic regression taking into consideration the depression diagnosis as well as age, sex, antihyperglycaemic medication, medication utilization, hospital admission and other comorbidities (from health insurance data).

RESULTS

Responders and non-responders did not differ in the depression diagnosis [OR 0.99, confidence interval (CI) 0.82-1.2]. Regardless of age and sex, treatment with insulin only (OR 1.73, CI 1.36-2.21), treatment with oral antihyperglycaemic drugs (OAD) only (OR 1.77, CI 1.49-2.09), treatment with both insulin and OAD (OR 1.91, CI 1.51-2.43) and higher general medication utilization (1.29, 1.10-1.51) were associated with responding to the survey.

CONCLUSION

We found differences in age, sex, diabetes treatment and medication utilization between responders and non-responders, which might bias the results. However, responders and non-responders did not differ in their depression status, which is the focus of the DiaDec study. Our analysis may serve as an example for conducting non-response analyses using health insurance data.

Drug utilization in the Maastricht Study: A comparison with nationwide data

Within the southern region of the Netherlands, the Maastricht Study is an on-going observational prospective population-based cohort study that focuses on the etiology of Type 2 diabetes mellitus (T2DM). Representativeness of the participating population is a crucial but often an unknown factor in population-based cohort studies such as the Maastricht Study. We therefore aimed to assess the representativeness of the study population by comparing drug utilization of the participants of the Maastricht Study with the general population of the Netherlands.Since T2DM patients were oversampled in this study, a sampling method was applied in order to ensure a similar distribution of T2DM over the study population. Drug use in the study population was compared with drug use in the population of the Netherlands, using a Z-test to compare 2 independent proportions.In general, drug use in the study was similar compared with national data. However, in the age group 65 to 74 years total drug use was lower in the study population (833/1000 persons) versus nationwide data (882/1000 persons). The use of pulmonary medications was lower (104/1000 persons vs 141/1000 persons) and the use of hypnotics/anxiolytics was higher (90/1000 persons vs 36/1000 persons) in the Maastricht Study as compared with national data.Drug use in the Maastricht Study population is largely comparable to that in the total Dutch population aged 45 to 74. Therefore, data on drug use by participants in the Maastricht Study can be used to perform studies assessing outcomes associated with drug use.

Evaluating selection bias in a population-based cohort study with low baseline participation: the LIFE-Adult-Study

Background

Participation in epidemiologic studies is steadily declining, which may result in selection bias. It is therefore an ongoing challenge to clarify the determinants of participation to judge possible selection effects and to derive measures to minimise that bias. We evaluated the potential for selection bias in a recent population-based cohort study with low baseline participation and investigated reasons for nonparticipation.

Methods

LIFE-Adult is a cohort study in the general population of the city of Leipzig (Germany) designed to gain insights into the distribution and development of civilisation diseases. Nine thousand one hundred forty-five participants aged 40–79 years were randomly sampled in 2011–2014. We compared LIFE-Adult participants with both the Leipzig population and nonparticipants using official statistics and short questionnaire data. We applied descriptive statistics and logistic regression analysis to evaluate the determinants of study participation.

Results

Thirty-one percent of the invited persons participated in the LIFE-Adult baseline examination. Study participants were less often elderly women and more often married, highly educated, employed, and current nonsmokers compared to both the Leipzig population and nonparticipants. They further reported better health than nonparticipants. The observed differences were considerable in education and health variables. They were generally stronger in men than in women. For example, in male study participants aged 50–69, the frequency of high education was 1.5 times that of the general population, and the frequency of myocardial infarction was half that of nonparticipants. Lack of time and interest, as well as health problems were the main reasons for nonparticipation.

Conclusions

Our investigation suggests that the low baseline participation in LIFE-Adult is associated with the typical selection of study participants with higher social status and healthier lifestyle, and additionally less disease. Notably, education and health status seem to be crucial selection factors. Consequently, frequencies of major health conditions in the general population will likely be underestimated. A differential selection related to sex might also distort effect estimates. The extent of the assessment, the interest in the research topic, and health problems of potential participants should in future be considered in LIFE-Adult and in similar studies to raise participation and to minimise selection bias.

Electronic supplementary material

The online version of this article (10.1186/s12874-019-0779-8) contains supplementary material, which is available to authorized users.

Healthcare provision, functional ability and quality of life after proximal femoral fracture - 'ProFem': Study protocol of a population-based, prospective study based on individually linked survey and statutory health insurance data

INTRODUCTION

Proximal femoral fractures (PFF) are among the most frequent fractures in older people. However, the situation of people with a PFF after hospital discharge is poorly understood. Our aim is to (1) analyse healthcare provision, (2) examine clinical and patient-reported outcomes (PROs), (3) describe clinical and sociodemographic predictors of these and (4) develop an algorithm to identify subgroups with poor outcomes and a potential need for more intensive healthcare.

METHODS AND ANALYSIS

This is a population-based prospective study based on individually linked survey and statutory health insurance (SHI) data. All people aged minimum 60 years who have been continuously insured with the AOK Rheinland/Hamburg and experience a PFF within 1 year will be consecutively included (SHI data analysis). Additionally, 700 people selected randomly from the study population will be consecutively invited to participate in the survey. Questionnaire data will be collected in the participants' private surroundings at 3, 6 and 12 months after hospital discharge. If the insured person considers themselves to be only partially or not at all able to take part in the survey, a proxy person will be interviewed where possible. SHI variables include healthcare provision, healthcare costs and clinical outcomes. Questionnaire variables include information on PROs, lifestyle characteristics and socioeconomic status. We will use multiple regression models to estimate healthcare processes and outcomes including mortality and cost, investigate predictors, perform non-responder analysis and develop an algorithm to identify vulnerable subgroups.

ETHICS AND DISSEMINATION

The study was approved by the ethics committee of the Faculty of Medicine, Heinrich-Heine-University Düsseldorf (approval reference 6128R). All participants including proxies providing written and informed consent can withdraw from the study at any time. The study findings will be disseminated through scientific journals and public information.

TRIAL REGISTRATION NUMBER

DRKS00012554.

Modelling attrition and nonparticipation in a longitudinal study of prostate cancer

Background

Attrition occurs when a participant fails to respond to one or more study waves. The accumulation of attrition over several waves can lower the sample size and power and create a final sample that could differ in characteristics than those who drop out. The main reason to conduct a longitudinal study is to analyze repeated measures; research subjects who drop out cannot be replaced easily. Our group recently investigated factors affecting nonparticipation (refusal) in the first wave of a population-based study of prostate cancer. In this study we assess factors affecting attrition in the second wave of the same study. We compare factors affecting nonparticipation in the second wave to the ones affecting nonparticipation in the first wave.

Methods

Information available on participants in the first wave was used to model attrition. Different sources of attrition were investigated separately. The overall and race-stratified factors affecting attrition were assessed. Kaplan-Meier survival curve estimates were calculated to assess the impact of follow-up time on participation.

Results

High cancer aggressiveness was the main predictor of attrition due to death or frailty. Higher Charlson Comorbidity Index increased the odds of attrition due to death or frailty only in African Americans (AAs). Young age at diagnosis for AAs and low income for European Americans (EAs) were predictors for attrition due to lost to follow-up. High cancer aggressiveness for AAs, low income for EAs, and lower patient provider communication scores for EAs were predictors for attrition due to refusal. These predictors of nonparticipation were not the same as those in wave 1. For short follow-up time, the participation probability of EAs was higher than that of AAs.

Conclusions

Predictors of attrition can vary depending on the attrition source. Examining overall attrition (combining all sources of attrition under one category) instead of distinguishing among its different sources should be avoided. The factors affecting attrition in one wave can be different in a later wave and should be studied separately.

Exploring patterns of response across the lifespan: the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) study

BACKGROUND

With declining rates of participation in epidemiological studies there is an important need to attempt to understand what factors might affect response. This study examines the pattern of response at different adult ages within a contemporary cross-sectional population-based cohort, the Cambridge Centre for Ageing and Neuroscience (Cam-CAN).

METHODS

Using logistic regression, we investigated associations between age, gender and Townsend deprivation level for both participants and non-participants. Weighted estimates of the odds ratios with confidence intervals for each demographic characteristic were calculated. Reasons given for refusal were grouped into three broad categories: 'active', 'passive' and illness preventing interview.

RESULTS

An association of age and participation was found, with individuals in middle age groups more likely to participate (age group 48-57 OR: 1.8, 95% CI: 1.5-2.2 and age group 58-67 OR: 2.1, 95% CI: 1.7-2.4). Overall, there was no difference in participation between men and women. An association with deprivation was found, with those living in the most deprived areas being the least willing to participate (fifth quintile OR: 0.6, 95% CI: 0.5-0.7). An interaction between age and gender was found whereby younger women and older men were more likely to agree to participate (p = 0.01).

CONCLUSION

Our findings highlight some of the factors affecting recruitment into epidemiological studies in the UK and suggest that targeted age-specific recruitment strategies might be needed to increase participation rates in future cohort investigations.

Response rates in case-control studies of cancer by era of fieldwork and by characteristics of study design

PURPOSE

The purpose of this study was to describe time trends in response rates in case-control studies of cancer and identify study design factors that influence response rate.

METHODS

We reviewed 370 case-control studies of cancer published in 12 journals during indicator years in each of the last four decades. We estimated time trends of response rates and reasons for nonresponse in each of the following types of study subjects: cases, medical source controls, and population controls. We also estimated response rates according to characteristics of study context.

RESULTS

Median response rates among cases and population controls were between 75% and 80% in the 1970s. Between 1971 and 2010, study response rates declined by 0.31% per year for cases and 0.78% for population controls. Only a minority of studies reported reasons for nonparticipation; subject refusal was the most common reported reason. Studies conducted in North America had lower median response rates than studies conducted in Europe. In-person and telephone interviews elicited higher response rates than mail questionnaires.

CONCLUSIONS

Response rates from case-control studies of cancer have declined, and this could threaten the validity of results derived from these studies.

Recruiting former melanoma patients via hospitals in comparison to office-based dermatologists in a register-based cohort study that required indirect contact

Background

There are detailed reviews about different recruitment strategies, but not with regard to differences between recruitment of hospital-based versus office-based physicians. Within this study, the two different recruitment schemes are compared. Advantages and disadvantages of different ways of recruitment in registry-based studies are discussed.

Methods

In a cross-sectional cancer-registry-based study, long-term melanoma patients were contacted by dermatologists rather than directly by the registry on the basis of the legal situation. Logistic regression models and generalized estimating equations were used to assess effects of various patient and physician characteristics on participation and data quality. Especially differences between hospital-based versus office-based dermatologists are evaluated.

Results

Seventy two out of 112 contacted dermatologists took part in the study (64.3%). The cooperation proportion was 52.2% (689 participants/1320 contacted patients). Participants and non-participants differed regarding age and sex, but not regarding other social demographic factors and cancer stage.

We did not observe a difference in patient participation between hospital-based versus office-based dermatologists (OR 1.08 [CI 0.84–1.39]; p = 0.57). However, medical data provided by the cancer registry were better for participants registered and recruited by hospitals.

Conclusions

In cohort studies with epidemiological cancer registries, recruitment via physicians has potential disadvantages and is more complex. If this indirect way of contact is mandatory, we recommend recruitment procedures including hospital-based rather than office-based physicians. However, physician characteristics were not associated with outcome.

Multiple Gene-Environment Interactions on the Angiogenesis Gene-Pathway Impact Rectal Cancer Risk and Survival

Characterization of gene-environment interactions (GEIs) in cancer is limited. We aimed at identifying GEIs in rectal cancer focusing on a relevant biologic process involving the angiogenesis pathway and relevant environmental exposures: cigarette smoking, alcohol consumption, and animal protein intake. We analyzed data from 747 rectal cancer cases and 956 controls from the Diet, Activity and Lifestyle as a Risk Factor for Rectal Cancer study. We applied a 3-step analysis approach: first, we searched for interactions among single nucleotide polymorphisms on the pathway genes; second, we searched for interactions among the genes, both steps using Logic regression; third, we examined the GEIs significant at the 5% level using logistic regression for cancer risk and Cox proportional hazards models for survival. Permutation-based test was used for multiple testing adjustment. We identified 8 significant GEIs associated with risk among 6 genes adjusting for multiple testing: TNF (OR = 1.85, 95% CI: 1.10, 3.11), TLR4 (OR = 2.34, 95% CI: 1.38, 3.98), and EGR2 (OR = 2.23, 95% CI: 1.04, 4.78) with smoking; IGF1R (OR = 1.69, 95% CI: 1.04, 2.72), TLR4 (OR = 2.10, 95% CI: 1.22, 3.60) and EGR2 (OR = 2.12, 95% CI: 1.01, 4.46) with alcohol; and PDGFB (OR = 1.75, 95% CI: 1.04, 2.92) and MMP1 (OR = 2.44, 95% CI: 1.24, 4.81) with protein. Five GEIs were associated with survival at the 5% significance level but not after multiple testing adjustment: CXCR1 (HR = 2.06, 95% CI: 1.13, 3.75) with smoking; and KDR (HR = 4.36, 95% CI: 1.62, 11.73), TLR2 (HR = 9.06, 95% CI: 1.14, 72.11), EGR2 (HR = 2.45, 95% CI: 1.42, 4.22), and EGFR (HR = 6.33, 95% CI: 1.95, 20.54) with protein. GEIs between angiogenesis genes and smoking, alcohol, and animal protein impact rectal cancer risk. Our results support the importance of considering the biologic hypothesis to characterize GEIs associated with cancer outcomes.

Unit Nonresponse in a Population-Based Study of Prostate Cancer

Low unit response rates can increase bias and compromise study validity. Response rates have continued to fall over the past decade despite all efforts to increase participation. Many factors have been linked to reduced response, yet relatively few studies have employed multivariate approaches to identify characteristics that differentiate respondents from nonrespondents since it is hard to collect information on the latter. We aimed to assess factors contributing to enrollment of prostate cancer (PCa) patients. We combined data from the North Carolina-Louisiana (LA) PCa Project's LA cohort, with additional sources such as US census tract and LA tumor registry data. We included specific analyses focusing on blacks, a group often identified as hard to enroll in health-related research. The ability to study the effect of Hurricane Katrina, which occurred amidst enrollment, as a potential determinant of nonresponse makes our study unique. Older age (≥ 70) for blacks (OR 0.65) and study phase with respect to Hurricane Katrina for both races (OR 0.59 for blacks, OR 0.48 for whites) were significant predictors of participation with lower odds. Neighborhood poverty for whites (OR 1.53) also was a significant predictor of participation, but with higher odds. Among blacks, residence in Orleans parish was associated with lower odds of participation (OR 0.33) before Katrina. The opposite occurred in whites, with lower odds (OR 0.43) after Katrina. Our results overall underscore the importance of tailoring enrollment approaches to specific target population characteristics to confront the challenges posed by nonresponse. Our results also show that recruitment-related factors may change when outside forces bring major alterations to a population's environment and demographics.

Explanation and Elaboration Document for the STROBE-Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary Extension

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers, and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples, and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet statement. Thus, this is a companion document to the STROBE-Vet statement methods and process document (JVIM_14575 "Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement" undergoing proofing), which describes the checklist and how it was developed.

Reasons for participation and non-participation in a randomized controlled trial: postal questionnaire surveys of women eligible for TOMBOLA (Trial Of Management of Borderline and Other Low-grade Abnormal smears)

Background Better understanding of motivators for, and barriers to, participation in randomized controlled trials (RCTs) in different study populations and settings has the potential to improve participation of historically under-represented groups (eg, women) in future trials.

Purpose To investigate reasons why women agreed, or declined, to participate in a RCT.

Methods In two postal questionnaire-based studies, we investigated women's reasons for participation or non-participation in TOMBOLA, a RCT comparing management policies for low-grade cervical abnormalities. Four-hundred and ninety-two TOMBOLA participants (response rate 56%) completed questionnaires on reasons for participation. One-hundred and thiry-seven women (38%) who declined TOMBOLA participation completed questionnaires on reasons for this.

Results Eighty percent of women reported that one of their reasons for attending their TOMBOLA recruitment appointment was worries about their smear result. Ninety-four percent participated in the RCT because it was a worthwhile contribution to the cervical screening programme and other women; for 70% this was the most important reason. These proportions did not vary by socio-demographic factors. Thirty-two percent thought participation would result in better care. The most common reason for non-participation was preference for follow-up from the woman's GP. Logistical issues (eg, inconvenient appointments, travel time, arranging time off work or child-care) were commonly cited. Fourteen percent were too frightened to participate; this was unrelated to the grade of the recruitment smear. Limitations Response rates were not high, but there was little evidence of response bias. Structured questionnaires were used.

Conclusions Future research should address how best to deliver information to ensure different social groups appreciate potential benefits of RCT participation and provide reassurance regarding fears about participation. Simple strategies (eg, appealing to the altruism of potential participants or offering flexible recruitment clinic locations and times) might enhance RCT recruitment rates. This in turn would ensure best use of research resources thus bringing the greatest benefits to participants and the population.

Risk factors for maternal injuries in a population-based sample of pregnant women

BACKGROUND

The prevalence of injuries during pregnancy is largely underestimated, as previous research has focused on more severe injuries resulting in emergency department visits and hospitalizations. The objective of our study was to estimate the frequency, risk factors, and causes of injuries in a population-based sample of pregnant women.

METHODS

This article is an analysis of postpartum interviews among the control series from a case-control study (n=1,488). Maternal, pregnancy, and environmental characteristics associated with injury during pregnancy in control subjects were examined to identify population-based risk factors for injury. We collected data on self-reported injury during pregnancy, including the month of pregnancy, whether medical attention was sought, the mechanism of injury, and the number and location of bodily injuries. Logistic regression was used to calculate unadjusted and adjusted odds ratios (aORs) of injury.

RESULTS

Over 5% of women reported an injury during pregnancy, with falls being the most common mechanism of injury. Women at highest adjusted risk for injury had unintended pregnancies (aOR: 2.28 [1.40-3.70]) and no partner during pregnancy (aOR: 2.45 [1.16-5.17]) relative to women without injuries.

CONCLUSIONS

Pregnant women with risk factors for many pregnancy-related complications are also at increased risk of injury during pregnancy. Further studies of pregnancy-related injuries are needed to consider environmental and maternal characteristics on risk of injury.

Participation rates, response bias and response behaviours in the community survey of the Swiss Spinal Cord Injury Cohort Study (SwiSCI)

Background

Surveying persons with disabilities is challenging, as targeted subjects may experience specific barriers to survey participation. Here we report on participation rates and response behaviour in a community survey of people with spinal cord injury (SCI) in Switzerland. The cross-sectional survey was implemented as part of the Swiss Spinal Cord Injury Cohort Study (SwiSCI) and represents the largest population-based SCI survey in Europe including nearly 2000 persons. Design features to enhance participation rates included the division of the questionnaire volume over three successive modules; recurrent and mixed-mode reminding of non-responders; and mixed-mode options for response.

Methods

We describe participation rates of the SwiSCI community survey (absolute and cumulative cooperation, contact, response, and attrition rates) and report on response rates in relation to recruitment efforts. Potential non-response bias and the association between responders’ characteristics and response behaviour (response speed: reminding until participation; response mode: paper-pencil vs. online completion) were assessed using regression modelling.

Results

Over the successive modules, absolute response rates were 61.1, 80.6 and 87.3 % which resulted in cumulative response rates of 49.3 and 42.6 % for the second and third modules. Written reminders effectively increased response rates, with the first reminder showing the largest impact. Telephone reminders, partly with direct telephone interviewing, enhanced response rate to the first module, but were essentially redundant in subsequent modules. Non-response to the main module was related to current age, membership of Swiss Paraplegic Association (SPA) and time since injury, but not to gender, lesion level and preferred language of response. Response speed increased with household income, but was not associated to other sociodemographic factors, lesion characteristics or health indicators. We found significant associations between online completion and male gender, younger age, higher education, higher income, SPA membership, tetraplegia, longer time since injury, higher quality of life, and more participation restrictions.

Conclusion

In this sample with little non-response bias, recurrent and mixed-mode reminding and mixed-mode options for response were key features of optimizing survey design.

Population-based multicase-control study in common tumors in Spain (MCC-Spain): rationale and study design

INTRODUCTION

We present the protocol of a large population-based case-control study of 5 common tumors in Spain (MCC-Spain) that evaluates environmental exposures and genetic factors.

METHODS

Between 2008-2013, 10,106 subjects aged 20-85 were enrolled in 23 hospitals and primary care centres in 12 Spanish provinces including 1,112 cases with a new diagnosis of prostate cancer, 1,738 of breast cancer, 2,140 of colorectal cancer, 459 of gastro-oesophageal cancer, 559 cases with chronic lymphocytic leukaemia and 4,098 population controls frequency matched to cases by age, sex and region of residence. Participation rates ranged from 57% (stomach cancer) to 87% (CLL cases) and from 30% to 77% in controls. Participants completed a face-to-face computerized interview on sociodemographic factors, environmental exposures, occupation, medication, lifestyle, and personal and family medical history. In addition, participants completed a self-administered food-frequency questionnaire and telephone interviews. Blood samples were collected from 76% of participants while saliva samples were collected in CLL cases and participants refusing blood extractions. Clinical information was recorded for cases and paraffin blocks and/or fresh tumor samples are available in most collaborating hospitals. Genotyping was done through an exome array enriched with genetic markers in specific pathways. Multiple analyses are planned to assess the association of environmental, personal and genetic risk factors for each tumor and to identify pleiotropic effects.

DISCUSSION

This study, conducted within the Spanish Consortium for Biomedical Research in Epidemiology & Public Health (CIBERESP), is a unique initiative to evaluate etiological factors for common cancers and will promote cancer research and prevention in Spain.

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.

Having children, social characteristics, smoking and the risk of uveal melanoma: a case-control study

PURPOSE

We analyzed data from the Risk Factors for Uveal Melanoma (RIFA) study to evaluate possible associations between uveal melanoma risk and having children, socioeconomic level and smoking.

METHODS

The RIFA study was a German case-control study conducted from September 2002 to March 2005. The study population consisted of 455 incident uveal melanoma patients (20-74 years of age) and 827 matched (age, sex, region of residence) population controls. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using conditional logistic regression.

RESULTS

Women with children showed an increased OR (1.59, 95% CI 0.95-2.66) for uveal melanoma development compared to women without children. We estimated decreased ORs for subjects with higher socioeconomic level compared to the lowest status (upper secondary school leaving certificate: OR 0.68, 95% CI 0.49-0.94; higher education: OR 0.60, 95% CI 0.38-0.96). Ever smokers showed an OR of 1.19 (95% CI 0.92-1.55) compared to never smokers.

CONCLUSION

The observed association between lower socioeconomic level and increased odds for uveal melanoma possibly represents a higher occupational uveal melanoma risk for occupational categories that are usually associated with lower socioeconomic status. Concerning having children and uveal melanoma development, we hypothesize that the observed association is mediated through alpha-melanocyte-stimulating hormone, a hormone that increases during pregnancy and is linked to pigmentation alterations in pregnant women.

Comparison of address-based sampling and random-digit dialing methods for recruiting young men as controls in a case-control study of testicular cancer susceptibility

Random-digit dialing (RDD) using landline telephone numbers is the historical gold standard for control recruitment in population-based epidemiologic research. However, increasing cell-phone usage and diminishing response rates suggest that the effectiveness of RDD in recruiting a random sample of the general population, particularly for younger target populations, is decreasing. In this study, we compared landline RDD with alternative methods of control recruitment, including RDD using cell-phone numbers and address-based sampling (ABS), to recruit primarily white men aged 18-55 years into a study of testicular cancer susceptibility conducted in the Philadelphia, Pennsylvania, metropolitan area between 2009 and 2012. With few exceptions, eligible and enrolled controls recruited by means of RDD and ABS were similar with regard to characteristics for which data were collected on the screening survey. While we find ABS to be a comparably effective method of recruiting young males compared with landline RDD, we acknowledge the potential impact that selection bias may have had on our results because of poor overall response rates, which ranged from 11.4% for landline RDD to 1.7% for ABS.

Cumulative exposure to paternal seminal fluid prior to conception and subsequent risk of preeclampsia

A growing body of literature suggests that prior and prolonged exposure to paternal antigens in seminal fluid induces maternal tolerance to the allogeneic fetus, protecting it from rejection and facilitating successful implantation and placentation. In this case-control study of nulliparous women, we test the hypothesis that increased exposure to paternal seminal fluid via the vaginal or oral route will confer a reduced risk of preeclampsia. Preeclampsia cases (n=258) and normotensive controls (n=182) were selected from live births to Iowa women over the period August 2002 to April 2005. Disease status was verified by medical chart review. Seminal fluid exposure indexes incorporated information on type and frequency of sexual practices, contraceptive use, and ingestion practices prior to conception with the baby's father. Preeclampsia risk decreased significantly with increasing vaginal exposure to paternal semen (test for trend p<0.05). Women in the highest 10th percentile of vaginal exposure had a 70% reduced odds of preeclampsia relative to women in the lowest 25th percentile of exposure (aOR=0.3; 95% CI: 0.1-0.9). Oral seminal fluid exposure was not associated with a reduced risk of preeclampsia. These findings are congruent with the immune maladaptation hypothesis of preeclampsia causation and indicate that paternal antigen exposure via the vaginal mucosa may facilitate immune tolerance to paternal HLA. Thus, advising nulliparous women to decrease their use of barrier contraceptive methods and to increase vaginal sexual intercourse prior to conceiving may reduce their risk of preeclampsia.

Risk of adult acute and chronic myeloid leukemia with cigarette smoking and cessation

BACKGROUND

Cigarette smoking is an established risk factor for adult myeloid leukemia, particularly acute myeloid leukemia (AML), but less is known about the nature of this association and effects of smoking cessation on risk.

METHODS

In a large population-based case-control study of myeloid leukemia that included 414 AML and 185 chronic myeloid leukemia (CML) cases and 692 controls ages 20-79 years, we evaluated risk associated with cigarette smoking and smoking cessation using unconditional logistic regression methods and cubic spline modeling.

RESULTS

AML and CML risk increased with increasing cigarette smoking intensity in men and women. A monotonic decrease in AML risk was observed with increasing time since quitting, whereas for CML, the risk reduction was more gradual. For both AML and CML, among long-term quitters (≥30 years), risk was comparable to non-smokers.

CONCLUSIONS

Our study confirms the increased risk of myeloid leukemia with cigarette smoking and provides encouraging evidence of risk attenuation following cessation.

Gene-diet-interactions in folate-mediated one-carbon metabolism modify colon cancer risk

SCOPE

The importance of folate-mediated one-carbon metabolism (FOCM) in colorectal carcinogenesis is emphasized by observations that high dietary folate intake is associated with decreased risk of colon cancer (CC) and its precursors. Additionally, polymorphisms in FOCM-related genes have been repeatedly associated with risk, supporting a causal relationship between folate and colorectal carcinogenesis.

METHODS AND RESULTS

We investigated ten candidate polymorphisms with defined or probable functional impact in eight FOCM-related genes (SHMT1, DHFR, DNMT1, MTHFD1, MTHFR, MTRR, TCN2, and TDG) in 1609 CC cases and 1974 controls for association with CC risk and for interaction with dietary factors. No polymorphism was statistically significantly associated with overall risk of CC. However, statistically significant interactions modifying CC risk were observed for DNMT1 I311V with dietary folate, methionine, vitamin B2 , and vitamin B12 intake and for MTRR I22M with dietary folate, a predefined one-carbon dietary pattern, and vitamin B6 intake. We observed statistically significant gene-diet interactions with five additional polymorphisms.

CONCLUSION

Our results provide evidence that FOCM-related dietary intakes modify the association between CC risk and FOCM allelic variants. These findings add to observations showing that folate-related gene-nutrient interactions play an important role in modifying the risk of CC.

Correction of systematic bias in ultrasound dating in studies of small-for-gestational-age birth: an example from the Iowa Health in Pregnancy Study

The authors examined whether early ultrasound dating (≤20 weeks) of gestational age (GA) in small-for-gestational-age (SGA) fetuses may underestimate gestational duration and therefore the incidence of SGA birth. Within a population-based case-control study (May 2002-June 2005) of Iowa SGA births and preterm deliveries identified from birth records (n = 2,709), the authors illustrate a novel methodological approach with which to assess and correct for systematic underestimation of GA by early ultrasound in women with suspected SGA fetuses. After restricting the analysis to subjects with first-trimester prenatal care, a nonmissing date of the last menstrual period (LMP), and early ultrasound (n = 1,135), SGA subjects' ultrasound GA was 5.5 days less than their LMP GA, on average. Multivariable linear regression was conducted to determine the extent to which ultrasound GA predicted LMP dating and to correct for systematic misclassification that results after applying standard guidelines to adjudicate differences in these measures. In the unadjusted model, SGA subjects required a correction of +1.5 weeks to the ultrasound estimate. With adjustment for maternal age, smoking, and first-trimester vaginal bleeding, standard guidelines for adjudicating differences in ultrasound and LMP dating underestimated SGA birth by 12.9% and overestimated preterm delivery by 8.7%. This methodological approach can be applied by researchers using different study populations in similar research contexts.

Medical conditions and risk of adult myeloid leukemia

PURPOSE

Although a few previous studies have reported positive associations between adult myeloid leukemia and a history of certain medical conditions, the etiology of most cases remains largely unknown. Our purpose was to examine associations between certain medical conditions and adult myeloid leukemia.

METHODS

Using logistic regression, we evaluated associations between 16 self-reported medical conditions and myeloid leukemia in a case-control study of 670 cases [including 420 acute myeloid leukemia (AML) and 186 chronic myelogenous leukemia (CML)] and 701 population-based controls.

RESULTS

We observed significant positive associations between AML and ulcerative colitis (odds ratio (OR) = 3.8; 95 % confidence interval (CI), 1.1-13) and between CML and peptic ulcer (OR = 2.0; 95% CI, 1.1-3.8). A personal cancer history increased both AML (OR = 2.6; 95% CI, 1.7-3.9) and CML (OR = 3.5; 95% CI, 2.0-5.8) risk even after excluding individuals who reported prior radiation and/or chemotherapy treatment.

CONCLUSION

Certain inflammatory medical conditions and a personal history of cancer, independent from therapy, are associated with an increased risk of myeloid leukemia.

Feasibility of neonatal dried blood spot retrieval amid evolving state policies (2009-2010): a Children's Oncology Group study

Dried blood spots (DBS) are collected uniformly from US newborns to test for metabolic and other disorders. Because evidence exists for prenatal origins of some diseases, DBS may provide unique prenatal exposure records. Some states retain residual DBS and permit their use in aetiological studies. The primary study aim was to assess the feasibility of obtaining residual DBS from state newborn screening programmes for paediatric and adolescent cancer patients nationwide with parental/subject consent/assent. Families of leukaemia and lymphoma patients aged ≤21 years diagnosed from 1998 to 2007 at randomly selected Children's Oncology Group institutions across the US were questioned (n = 947). Parents/guardians and patients aged ≥18 years were asked to release DBS to investigators in spring 2009. DBS were then requested from states. Overall, 299 families (32%) released DBS. Consenting/assenting patients were born in 39 US states and 46 DBS were obtained from five states; 124 DBS were unobtainable because patients were born prior to dates of state retention. State policies are rapidly evolving and there is ongoing discussion regarding DBS storage and secondary research uses. Currently, population-based DBS studies can be conducted in a limited number of states; fortunately, many have large populations to provide reasonably sized paediatric subject groups.

Nonsteroidal anti-inflammatory drug and acetaminophen use and risk of adult myeloid leukemia

BACKGROUND

Little is known about the causes of adult leukemia. A few small studies have reported a reduced risk associated with regular use of nonsteroidal anti-inflammatory drugs (NSAID).

METHODS

In a population-based case-control study, we evaluated analgesic use among 670 newly diagnosed myeloid leukemia cases [including 420 acute myeloid leukemias (AML) and 186 chronic myeloid leukemias (CML)] and 701 controls aged 20 to 79 years. Prior use of aspirin, ibuprofen, acetaminophen, other NSAIDs, and COX-2 inhibitors was assessed and included frequency, duration, and quantity. ORs and 95% CIs were calculated using unconditional logistic regression adjusting for potential confounders.

RESULTS

Regular/extra strength aspirin use was inversely associated with myeloid leukemia in women (OR = 0.59, 95% CI = 0.37-0.93) but not in men (OR = 0.85, 95% CI = 0.58-1.24). In contrast, acetaminophen use was associated with an increased risk of myeloid leukemia in women only (OR = 1.60, 95% CI = 1.04-2.47). These relationships were stronger with increasing dose and duration. When stratified by leukemia type, aspirin use was inversely associated with AML and CML in women. No significant overall associations were found with ibuprofen or COX-2 inhibitors for either sex; however, a decreased risk was observed with other anti-inflammatory analgesic use for women with AML or CML (OR = 0.47, 95% CI = 0.22-0.99; OR = 0.31, 95% CI = 0.10-0.92, respectively).

CONCLUSIONS

Our results provide additional support for the chemopreventive benefits of NSAIDs, at least in women. Because leukemia ranks fifth in person-years of life lost due to malignancy, further investigation is warranted.

IMPACT

NSAIDs may reduce, whereas acetaminophen may increase, myeloid leukemia risk in women.

Non-response bias in a surveillance program for asbestos-related lung cancer

OBJECTIVES

In a cohort study non-response might lead to a biased selection of cohort members and may affect the validity and reliability of the study outcome. To detect the possible effects of a non-response bias on study results, we evaluated the reasons for non-participation and the differences of respondents and non-respondents in a health surveillance program for power industry workers, formerly exposed to asbestos.

METHODS

A cohort of former power plant workers was formed to participate in an early detection program for lung cancer. We evaluated the results of 1,019 individuals (mean age 66 yr), of which 839 took part in at least one examination, 180 refused to participate or did not respond. To obtain the reasons for non-response, we interviewed the cohort members by telephone or we requested them by mail to complete and return a brief questionnaire. Further sources of information were the communal registration offices and local health offices.

RESULTS

The main reasons for non-participation were refusal (35%), illness (23.3%), death (16.7%) and difficulties with traveling (13.3%). It was impossible to make contact with or obtain an explanation from 11.7%. In a logistic regression model we demonstrated that advanced age and a long travel distance from the study center negatively affected the participation rate (p<0.001). There was no difference between respondents and non-respondents regarding prevalence (p=0.559) and incidence of lung cancer (p=0.882).

CONCLUSION

We concluded that in our cohort non-participation did not cause a selection bias in terms of lung cancer rates.

A case-control study: occupational cooking and the risk of uveal melanoma

Background

A European-wide population based case-control study (European rare cancer study) undertaken in nine European countries examined risk factors for uveal melanoma. They found a positive association between cooks and the risk of uveal melanoma. In our study we examine whether cooks or people who worked in cook related jobs have an increased uveal melanoma risk.

Methods

We conducted a case-control study during 2002 and 2005. Overall, 1653 eligible subjects (age range: 20-74 years, living in Germany) participated. Interviews were conducted with 459 incident uveal melanoma cases, 827 population controls, 180 ophthalmologist controls and 187 sibling controls. Data on occupational exposure were obtained from a self-administered postal questionnaire and a computer-assisted telephone interview. We used conditional logistic regression to estimate odds ratios adjusting for the matching factors.

Results

Overall, we did not observe an increased risk of uveal melanoma among people who worked as cooks or who worked in cook related jobs. When we restricted the source population of our study to the population of the Federal State of Northrhine-Westphalia, we observed an increased risk among subjects who were categorized as cooks in the cases-control analysis.

Conclusion

Our results are in conflict with former results of the European rare cancer study. Considering the rarity of the disease laboratory in vitro studies of human uveal melanoma cell lines should be done to analyze potential exposure risk factors like radiation from microwaves, strong light from incandescent ovens, or infrared radiation.

Invited commentary: Evaluating epidemiologic research methods--the importance of response rate calculation

Epidemiologic research that uses administrative records (rather than registries or clinical surveys) to identify cases for study has been increasingly restricted because of concerns about privacy, making unbiased population-based research less practicable. In their article, Nattinger et al. (Am J Epidemiol. 2010;172(6):637-644) present a method for using administrative data to contact participants that has been well received. However, the methods employed for calculating and reporting response rates require further consideration, particularly the classification of untraceable cases as ineligible. Depending on whether response rates are used to evaluate the potential for bias to influence study results or to evaluate the acceptability of the method of contact, different fractions may be considered. To improve the future study of epidemiologic research methods, a consensus on the calculation and reporting of study response rates should be sought.

Infant leukemia and congenital abnormalities: a Children's Oncology Group study

BACKGROUND

Leukemia in infants is rare and has not been well studied apart from leukemia in older children. Differences in survival and the molecular characteristics of leukemia in infants versus older children suggest a distinct etiology, likely involving prenatal factors.

PROCEDURE

We examined the association between eight categories of maternally reported congenital abnormalities (CAs) (cleft lip or palate, spina bifida or other spinal defect, large or multiple birthmarks, other chromosomal abnormalities, small head or microcephaly, rib abnormalities, urogenital abnormalities, and other) and infant leukemia in a case-control study. The study included 443 cases diagnosed at <1 year of age at a Children's Oncology Group Institution in the United States or Canada from 1996 to 2006 and 324 controls. Controls were recruited from the cases' geographic area either by random digit dialing (1999-2002) or through birth certificates (2003-2008) and were frequency-matched to cases on birth year. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by unconditional logistic regression after adjustment for birth year and a measure of follow-up time to account for differences in the CA observation period.

RESULTS

No statistically significant associations were observed between infant leukemia and any CA (OR = 1.2; 95% CI: 0.8-1.9), birthmarks (OR = 1.4; 95% CI: 0.7-2.5), urogenital abnormalities (OR = 0.7; 95% CI: 0.2-2.0), or other CA (OR = 1.4; 95% CI: 0.7-2.8). Results were similar for acute lymphoblastic and myeloid leukemia cases. Fewer than five subjects were in the remaining CA categories precluding analysis.

CONCLUSIONS

Overall, we did not find evidence to support an association between CAs and infant leukemia.

Prevalence of intimate partner violence among an abortion clinic population

In this cross-sectional, clinic-based study, we estimated 1-year prevalence of intimate partner violence among 986 patients who had elective abortions. We assessed physical, sexual, and battering intimate partner violence via self-administered, computer-based questionnaires. Overall, physical and sexual intimate partner violence prevalence was 9.9% and 2.5%, respectively; 8.4% of those in a current relationship reported battering. Former partners perpetrated more physical and sexual assaults than did current partners. Violence severity increased with frequency. Abortion patients experience high intimate partner violence rates, indicating the need for targeted screening and community-based referral.

Infant leukemia and parental infertility or its treatment: a Children's Oncology Group report

BACKGROUND

Little is known about the potential risk factors for infant leukemia. With its very young age at diagnosis, exposures occurring in the perinatal period are suspected. Parental infertility and infertility treatment have been studied with regard to childhood cancer in general, but rarely in individual cancer subtypes.

METHODS

A case-control study of infant leukemia was conducted through the Children's Oncology Group, including cases diagnosed from January 1996 to December 2006 and controls selected through random digit dialing and birth certificate tracing. Maternal phone interviews were conducted to obtain information about infertility, infertility treatment and demographic factors. All cases as well as subgroups defined by mixed lineage leukemia (MLL) translocation status and leukemia subtype were examined. Statistical analysis was performed using multivariate logistic regression models.

RESULTS

No significant associations between infertility or its treatment and combined infant leukemia were found. In subgroup analyses, there was a significant increase in the risk of MLL--leukemia for children born to women not trying to conceive compared with those trying for <1 year for all types combined [odds ratio (OR) = 1.62, 95% confidence interval (CI) = 1.01-2.59] and for acute lymphoblastic leukemia (OR = 2.50, 95% CI = 1.36-4.61).

CONCLUSIONS

There were no positive associations between parental infertility or infertility treatment and infant leukemia. While this is the largest study to date, both selection and recall bias may have impacted the results. However, for infant leukemia, we can potentially rule out large increases in risk associated with parental infertility or its treatment.

Comparability and representativeness of control groups in a case-control study of infant leukemia: a report from the Children's Oncology Group

Traditionally, controls in US pediatric cancer studies were selected through random digit dialing. With declining participation and lack of nonparticipant information, random digit dialing (RDD) controls may be substandard. Birth certificate (BC) controls are an alternative, because they are population based and include data from nonparticipants. The authors examined controls collected by random digit dialing and birth certificates for a Children's Oncology Group case-control study of infant leukemia in 1995-2006. Demographic variables were used to assess differences in RDD and BC controls and their representativeness. RDD and BC controls did not differ significantly with regard to maternal variables (age, race, education, marital status, alcohol during pregnancy) or child variables (sex, gestational age, birth weight), but they varied in smoking during pregnancy (22% RDD controls, 12% BC controls) (P = 0.05). The study's combined control group differed significantly from US births: Mothers of controls were more likely to be older (29.8 vs. 27.2 years), white (84% vs. 59%), and married (85% vs. 67%) and to have >16 years of education (37% vs. 25%). Control children were more often full term (88% vs. 81%) and heavier (3,436 vs. 3,317 g). Finally, participating BC mothers were likely to be older and to have more education than nonparticipants. Thus, the study's control groups were comparable but differed from the population of interest.

Dietary patterns and colon cancer risk in Whites and African Americans in the North Carolina Colon Cancer Study

We examined associations of dietary patterns with colon cancer risk in African Americans and Whites from a case-control study in North Carolina. Incident colon cancer cases, 40 to 80 yr (n = 636), and matched controls (n = 1,042) were interviewed in person to elicit information on potential colon cancer risk factors. A validated food frequency questionnaire adapted to include regional foods captured diet over the year prior to diagnosis (cases) or interview date (controls). Three meaningful intake patterns were identified in both Whites and African Americans: "Western-Southern," "fruit-vegetable," and "metropolitan." Compared to the Western-Southern pattern, the fruit-vegetable and metropolitan patterns were associated with more healthful dietary behaviors (e.g., higher vegetable intake and lower red meat consumption), and demographic/lifestyle characteristics typically correlated with low colon cancer risk, for example, lower BMI, higher education, and higher NSAID use. The fruit-vegetable pattern was significantly inversely associated with colon cancer risk in Whites (OR = 0.4, 95% CI = 0.3-0.6) and the metropolitan pattern with a nonsignificant 30% risk reduction in both Whites and African Americans after adjustment for education. The Western-Southern pattern was not associated with colon cancer risk. These findings may explain some of the racial differences in colon cancer incidence and underscore the importance of examining diet-cancer associations in different population subgroups.

[Strengthening the reporting of observational studies in epidemiology (STROBE): explanation and elaboration]

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.

Positive interaction between light iris color and ultraviolet radiation in relation to the risk of uveal melanoma: a case-control study

PURPOSE

To examine the association among phenotypic characteristics, chronic and intermittent ultraviolet (UV) radiation, and the risk of uveal melanoma.

DESIGN

Case-control study.

PARTICIPANTS

Overall, between September of 2002 and March of 2005, 1677 eligible subjects (age range: 20-74 years, living in Germany) participated. Interviews were conducted with 459 incident uveal melanoma cases (response proportion 94%), 827 population controls (55%), 180 ophthalmologist controls (52%), and 187 sibling controls (57%).

METHODS

Data on phenotypic characteristics and chronic and intermittent UV radiation exposure were obtained from a self-administered postal questionnaire and computer-assisted telephone interview. We used conditional logistic regression to estimate odds ratios adjusting for the matching factors. Furthermore, we studied the presence of synergy (super additive of risk or relative excess risk due to interaction) between light iris color and several UV radiation exposures.

MAIN OUTCOME MEASURES

Hair color at age 20 years, eye color, untanned skin color, ability to tan, propensity to burn on exposure, freckling, occupational sun exposure, artificial UV radiation, burns to the eyes.

RESULTS

In all 3 control groups, fair skin color, freckling as a child, nevi on the upper arms, burns to the eyes, use of sunlamps, and ever worked outside for 4 or more hours per day were positively associated with uveal melanoma. The association with eye color was apparent only in population controls (odds ratio = 1.9; 95% confidence interval [CI], 1.4-5.2), resulting in a relative excess risk due to interaction of 0.9 (95% CI, -0.6-2.3) for light iris color and more than 5 eye burns (UV-related keratitis) and 0.6 (95% CI, -0.3 to 1.5) for light iris color and eye protection.

CONCLUSIONS

Our interaction analyses suggest that there is an etiologic synergism between light iris color and the exposure of UV radiation. People with light iris color may have an especially increased risk for uveal melanoma if they are exposed to UV radiation.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Participation in pediatric epidemiologic research: the SEARCH for Diabetes in Youth Study experience

BACKGROUND

We evaluated the association of demographic and clinical characteristics with participation in an epidemiologic study of diabetes mellitus among youth.

METHODS

SEARCH for Diabetes in Youth is a multicenter study of physician-diagnosed diabetes in youth under the age of 20 comprising a surveillance and a cohort component. At each center, we enumerated all prevalent cases of diabetes in 2001 (n=6266) and all incident cases between 2002 and 2004 (n=3668). After confirmation of eligibility and validation, we invited each case to complete a survey and participate in a study visit. Here we evaluate how age, sex, race, and diabetes type are associated with participation in the survey and study visit.

RESULTS

Among prevalent cases, participation in the survey was 68% and 41% in the study visit. Among 2002 to 2004 incident cases, participation varied for the survey (76%, 81%, and 82%) and study visit (52%, 60%, and 60%). In multivariate logistic regression analyses among all incident cases, older age was associated with a lower odds of participation in the study visit (15-17 vs. <10 years: OR 0.5, 95% CI 0.4-0.7; 18-19 vs. <10 years: OR 0.3, 95% CI 0.2-0.5), as was having type 2 diabetes vs. type 1 diabetes (OR 0.5, 95% CI 0.4-0.7) and being of African American race vs. non-Hispanic White (OR 0.6, 95% CI 0.4-0.8). Results were very similar among prevalent cases.

CONCLUSIONS

Elucidating the relationship between individual characteristics and participation is essential for evaluating nonresponse bias, correcting for it, and for planning and implementing recruitment strategies.

Who are we missing? Area deprivation and survey participation

This study investigates selective participation by area deprivation in two population-based, nationally-representative surveys of children aged 5-16 years in England. We analysed the English participants (N = 22,903) in the British Child and Adolescent Mental Health Surveys, conducted in 1999 and 2004. The surveys recruited parents, teachers and children, allowing us to calculate participation rates for all three types of informant, with particularly detailed analyses possible for parents. Area-deprivation was assigned using Indices of Multiple Deprivation, 2004. We found that parents, teachers and children from more deprived areas were all substantially less likely to participate, with participation 8-9% lower in the most deprived areas than in the least deprived areas. There was substantial heterogeneity in the effect of deprivation on different types of parental non-participation, with a strong association for overall non-contact but none for overall non-cooperation. Refusal to participate in response to opt-out letters showed the opposite gradient to all other forms of non-participation, with individuals from less deprived areas being more likely to opt out. These findings indicate that the deprivation level of area of residence predicts non-response in multiple types of informants, which may exacerbate bias when estimating the prevalence of health outcomes. Furthermore, the magnitude and the direction of this may depend on the recruitment method used. Differential response by area deprivation may therefore be worth measuring in any survey.

Knowledge about infection with human papillomavirus: a systematic review

OBJECTIVE

Human papillomavirus (HPV) is a necessary cause of cervical cancer and genital warts. The aim of this systematic literature review was to provide an overview of knowledge about HPV infection among the public, students, patients and health professionals.

METHOD

PubMed searches were performed and the results of studies were reported by age, gender, study population, country, recruitment score and year of study conduct. The recruitment score covered the mode of recruitment, study size and response rate.

RESULTS

We included 39 studies published between 1992 and 2006 covering a total of 19,986 participants. The proportion of participants who had heard of HPV varied from 13% to 93%. Understanding that HPV is a risk factor for cervical cancer depended on whether the question was closed (8-68%) or open (0.6-11%). Between 5% and 83% knew about the association of HPV and (genital) warts. HPV was often mistaken with other sexually transmitted viruses. Health professionals and women had better knowledge about HPV than other participants.

CONCLUSION

Overall, the knowledge of the general public about HPV infection is poor. Efforts should be increased to give sufficient and unbiased information on HPV infection to the general public.

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration

Much medical research is observational. The reporting of observational studies is often of insufficient quality. Poor reporting hampers the assessment of the strengths and weaknesses of a study and the generalisability of its results. Taking into account empirical evidence and theoretical considerations, a group of methodologists, researchers, and editors developed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations to improve the quality of reporting of observational studies. The STROBE Statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results and discussion sections of articles. Eighteen items are common to cohort studies, case-control studies and cross-sectional studies and four are specific to each of the three study designs. The STROBE Statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This explanatory and elaboration document is intended to enhance the use, understanding, and dissemination of the STROBE Statement. The meaning and rationale for each checklist item are presented. For each item, one or several published examples and, where possible, references to relevant empirical studies and methodological literature are provided. Examples of useful flow diagrams are also included. The STROBE Statement, this document, and the associated Web site (http://www.strobe-statement.org/) should be helpful resources to improve reporting of observational research.